The image data receiving means generally used in mammography are x-ray films placed in cassettes. Such cassettes are available in several different types, depending e.g. on the manufacturer of the cassette and the type of imaging the cassette is designed for. Often there are also differences between cassettes according to whether the film used in them is intended to be developed in a darkroom or e.g. in a special film development device. These so-called daylight cassettes are gradually replacing darkroom cassettes. In this field, many kinds of devices for the loading of cassettes with a film and for the removal of the film from cassettes have been developed, and likewise different labeling devices, i.e. devices e.g. for printing or exposing patient information and imaging parameters on the film in a cassette.
The imaging apparatus used in mammography generally have in their imaging area a space with at least one feed/eject opening, a cassette tunnel or equivalent, into which a cassette loaded with a film is entered and where it is positioned at a desired imaging position and from where it is removed and taken to a separate labeling stage. In many imaging apparatus, the cassette tunnel is so implemented that its open end or ends form a cassette feed/eject opening. When both ends of the tunnel are open, the cassette can be moved in the tunnel by pushing it from one end of the tunnel and pulling from the other. Moreover, in some devices the tunnel wall is provided with additional holes to make it easier to move the cassette.
However, handling the cassette in such a cramped tunnel, besides being difficult and awkward, is also time-consuming. Especially in mammographic screening studies, in which the cassette may have to be changed as many as 50 times an hour, cassette handling alone takes up a considerable amount of time, and for an individual patient this means that the imaging operation, which many patients find unpleasant, takes an annoyingly long time.
Traditionally, mammography apparatus have been used to take various individual transillumination radiographs. However, the information given by a transillumination radiograph is not always sufficient in a diagnostic sense. For this reason, there has been a trend in recent times towards discovering new imaging methods e.g. to make different layers in the tissue under imaging more clearly visible in the images. A contribution to this development has been the progress in the technology and prices of digital sensors toward a level that is beginning to enable their use in mammography apparatus, too, both in an economic sense and in respect of image quality and authority approval.
In many imaging modes that are more complex than transillumination imaging, a requirement is that it should be possible to change in some way the position of the object to be imaged with respect to the imaging means during the imaging process. Such a change can be implemented either as a stepwise action or as a continuous movement during imaging. When controlled movement of the object to be imaged is difficult to achieve, as is the case in mammography, one can naturally seek for means for moving the imaging means.
Prior-art mammography apparatus have means for moving the imaging means in relation to the object to be imaged e.g. to change the height position of the imaging means in relation to the object to be imaged, means for interdependently revolving the imaging means around the object to be imaged, and means for inclining the radiation source in relation to the object to be imaged and the image data receiving means. As for other movements, certain apparatus also have means for moving e.g. a screen placed near the radiation source to define the radiation beam in a desired manner, and even means for moving the object to be imaged during the imaging process. However, independent movements of image data receiving means that may be needed during imaging have been difficult to implement in a desired manner because, if the structure of the apparatus has permitted such movements at all, they have had to be carried out manually.
In some mammography apparatus, difficulties have been encountered in getting the cassette correctly positioned in the imaging area. If the cassette is in the wrong position, this may result in leaving part of the tissue to be imaged outside the area of which an image is formed on the film or other receiving medium, which may necessitate renewal imaging. This creates extra work and an unnecessary additional exposure of the tissue to radiation.
Often the actions requiring handling of the cassette in the cassette tunnel have to be performed in ergonomically difficult working positions. This is the case especially when more than one image is taken of the same object, possibly even on the same film, in which case the cassette has to be changed or moved to a new position in the cramped cassette tunnel while the object to be imaged may remain positioned during all this time, in mammography in practice generally compressed between the compression plates of the imaging apparatus.
Recording patient information, dates, imaging parameters and projections etc. on the film or equivalent is an essential part of the imaging process. Especially in mammographic screening studies referred to above, there is a great risk of labeling errors occurring due to human factors. When the actions related to labeling are carried out as an operation physically separate from the actual imaging process, the cassettes may be interchanged when being taken from the imaging apparatus to the labeling station. Thus, information of a wrong patient and/or wrong imaging parameters may be entered on the film. And when human activities are concerned, it may even happen that some or even all of the data is not recorded at all when the labeling of an individual cassette or a whole batch of cassettes is accidentally neglected e.g. as a result of a lapse of memory. On the whole, labeling the films is an operation that requires accurate management and contributes for its part to the total duration of the imaging process.